Synthetic porphyrins and metalloporphyrins have become increasingly important in numerous and diverse technical fields. Their several practical applications include their use as sensitizers in photodynamic therapy (PDT) (Mody, (2000) J. Porphyrins Phthalocyanines 4: 362); in electron transfer (Lippard and Berg, (1994) Principles of Bioinorganic Chemistry, University Science Book: Mill Valley, Calif.); in DNA strand cleavage (Bennett et al., (2000) Proc. Natl. Acad. Sci. 97: 9476; Hashimoto et al., (1983) Tetrahedron letters, 24: 1523); as carriers of cytotoxic anticancer drugs such as platinum (Song et al., (2002) Inorganic Biochemistry 83: 83; and Lottner et al. (2002) J. Med. Chem., 45, 2064); as components of synthetic receptors (Jain and Hamilton, (2002) Org. Lett. 2: 1721); and as oxidation catalysts (Guo et al. (2001) J. Mol. Catal. A Chem. 170: 43). Additionally, functionalized porphyrins have become important leads in current drug discovery techniques (See Mody, supra, and Priola et al., (2002) Science 287: 1503). Accordingly, the development of new methodologies and strategies to improve the synthesis of functionalized porphyrins has become highly desirable.
Numerous methods for the synthesis of porphyrins are known. The classical methods for porphyrin synthesis typically require harsh reaction conditions and can provide disappointingly low yields (Rothemund, (1935) J. Am. Chem. Soc., 57: 2010; Adler et al., (1967) J. Org. Chem. 32: 476). Newer methodologies, such as those developed by Lindsey and colleagues, have resolved certain issues regarding reaction conditions and yields (Lindsey et al., (1987) J. Org. Chem. 52: 827). More recently, transition metal-catalyzed organic synthesis methodologies (e.g., Suzuki coupling and Heck-type coupling), have been successfully employed with porphyrin systems, providing versatile and general synthetic approaches for the preparation of a variety of functionalized porphyrins and porphyrin analogs. See, e.g., DiMagno et al., (1993) J. Org. Chem., 58: 5983; DiMagno, et al. (1993) J. Org. Chem. 115: 2513; Chan, et al., (1995) Tetrahedron 51: 3129; Zhou et al., (1996) J. Org. Chem. 61: 3590; Risch and Rainer, (1997) Tetrahedron Letters 38: 223; Hyslop et al., (1998) Am. Chem. Soc. 120: 12676; Boyle and Shi, (2002) J. Chem. Soc. Pekin Trans., 1: 1397; and Pereira, et al., (2002) J. Chem. Soc. Pekin Trans., 2: 1583. See also, Suzuki, (1998) Metal-Catalyzed Cross-Coupling Reactions, pp. 49-97, Wiley-VCH, Weinheim, Germany; U.S. Pat. No. 5,550,236 and U.S. Pat. No. 5,756,804, which references are incorporated herein by reference.
However, each of these foregoing methods possesses undesirable aspects that should be mitigated, including incompatibilities between catalysts and reaction compounds, low turnover number (TON) and low turnover frequency (TOF). Thus, despite recent advances in porphyrin chemistry, a need still exists for facile and general syntheses for, in particular, heteroatom-substituted porphyrins and metalloporphyrins.